1. Field of the Invention
The present invention relates to quartz glass and a quartz glass jig for use in producing a semiconductor and having excellent plasma corrosion resistance, and to a method for producing any one of the quartz glass and the quartz glass jig.
2. Description of the Related Art
In such production of the semiconductor, for example, in the production of a semiconductor wafer, in accordance with a recent trend in increasing a diameter thereof, an improvement of processing efficiency is performed by using a plasma reaction apparatus in an etching process and the like. For example, in a process of etching the semiconductor wafer, an etching treatment is performed by using a plasma gas such as a fluorine (F)-based plasma gas.
However, when conventional quartz glass is placed, for example, in an F-based plasma gas atmosphere, SiO2 and the F-based plasma gas are allowed to react with each other on a surface of the quartz glass, to thereby generate SiF4. Since a boiling point of the thus-generated SiF4 is −86° C., it is easily sublimated and, then, the quartz glass is corroded to a great extent causing a reduction in thickness or roughening the surface thereof. Thus, the quartz glass was found to be unsuitable for use as a jig in an atmosphere of the F-based plasma gas.
As described above, in the conventional quartz glass, a serious problem was generated in corrosion resistance, namely, plasma corrosion resistance, in a plasma reaction at the time of producing the semiconductor, particularly, an etching treatment using the F-based plasma gas. Under these circumstances, proposals in which aluminum or an aluminum compound covers a surface of a quartz glass member to improve the plasma corrosion resistance (refer to JP1997-95771A, JP1997-95772A and JP1998-139480A) or another proposal for plasma corrosion resistant glass in which aluminum is allowed to be contained in quartz glass to improve the plasma corrosion resistance (JP1999-228172A) have been made.
According to the present technique, quartz glass was prepared by heat-fusing a quartz glass powder mixed with 5 wt % of alumina powder in vacuum. The plasma corrosion resistance of the thus-prepared quartz glass was investigated. As a result, an etching rate thereof was reduced by 40% to 50% compared with a quartz glass member without containing any dopant at all.
As a reason for that, it is assumed that a boiling point of AlF3 that is generated on the reaction with the F-based plasma gas is 1290° C. that is far higher than that of SiF4. Therefore it is considered that, while a SiF4 portion is corroded to a great extent, sublimation on a surface of an AlF3 portion occurs to a small extent and, accordingly, a difference in an etched quantity becomes large therebetween.
In a same way of thinking, quartz glass containing 0.1 to 20 wt % of a total of two types or more of metallic elements which comprises a first metallic element that is a type belonging to 3B of the periodic table and a second metallic element that is at least one type selected from the group consisting of Zr, Y, lanthanoids and actinoids is also proposed (JP2002-220257A).
The first and second metallic elements contained in the above-described quartz glass each have a higher boiling point in a fluoride form thereof than that of Si, to thereby reduce an etching rate. For example, since a boiling point of NdF3 is 2327° C., when the plasma corrosion resistance is investigated, the etching rate thereof has reduced by 50% to 70% as compared with that of the quartz glass member without containing any dopant at all.